Coated ferromagnetic core element



May 27, 1952 F. H. GusDoRF 2,598,371

COATED FERROMAGNETIC com: ELEMENT Filed Sept. 19, 1945 BVM/M Patented May 27, 1952 COATED FERROMAGNETIC CORE ELEMENT Frederik Hendrik Gusdorf, Eindhoven, Netherlands, assigner to Hartford National Bank & Trust Co., Hartford, Conn., as trustee Application September 19, 1945, Serial No. 617,437 In the Netherlands May 7, 1943 section 1, rubin#I Law 69o, August s, 194s Patent expires May 7, 1963 l Claims. l

The invention relates to magnetic cores consisting of a mass of ferrite which has rbee sintered together.

In an earlier patent specification of the applicant, which had not yet been published at the date of priority of the present patent specication, is described that if in the manufacture of such a core care is taken to ensure that the ferrite has a suiiicient content of oxygen it is possible to manufacture cores which, in the case of a low induction, give rise to very low total electric losses (eddy current losses, hysteresis losses and other losses), even at higher frequencies. Such cores are therefore very suitable for radio, telegraphy and telephony purposes, for example for the manufacture of pupin coils, lter coils, slidable-core coils, etc. With a sufficiently high content of oxygen it is possible to obtain ferrites for which the value of the loss coefficient tgt is less than 0.06 at the said high frequencies, in y wherein R, L and w represent the loss resistance, the self-induction measured on a coil Wound on an annular core of ferrite and the frequency expressed in radians respectively.

Now it has been found that with the practical use of a coil comprising a magnetic core consistlng of a mass of ferrite which has been sintered together, the value of the electric losses may vary in course of time and that, more particularly at high frequencies, appreciable variations may occur.

The invention, which has for its object to obviate this drawback, is based on the recognition that these fluctuations in the Value of the electric losses are connected with the content of moisture of the core and that, when moisture is taken up by the core from the ambient atmosphere, the electric losses increase.

According to the invention, a magnetic core consisting of ferrite is provided with a moistureretaining envelope. It is evident that before this envelope is provided the core must be dried satisfactorily.

A moisture-retaining envelope may be obr tained, for example, by immersing a core in a liqueed or softened electric insulating material mentioned magnetic cores with low loss values which are destined to be utilized for radio, telegraphy and telephony purposes. It is particularly important for magnetic ferrite cores wherein a sufciently high content of oxygen, which is desirable in view of the electric losses, is ensured by causing the ferrite, after its formation, to take up oxygen, for in order to promote an easier absorption of oxygen use is preferably made of an open structure which is readily accessible to oxygen.

It has been found that cores having such a porous structure may be particularly sensitive to moisture. The use of a moisture-retaining envelope according to the invention is therefore of great importance for these cases. In these cases the core is preferably impregnated, for example in vacuo, with an electrically insulating material which can readily be softened, such as paraffin, petrolatum, ozokerite, in such manner that the impregnating agent penetrates as far as possible into the pores. A core thus protected against the action of moisture may retain practically unlimitedly the same constant value of the electric losses.

In order that the invention can |be more readily understood and carried into effect, it will now be described with reference to the accompanying drawing in which an inductance element containing a core element according to the invention is shown partially in section.

Referring more particularly to the drawing, a porous core element I comprising a sintered body of ferrite material is enclosed in a moisture ei:- cluding envelope 2 of Vaseline or paraffin Wax which has been impregnated into the porous structure in order to obtain a moisture excluding seal around the core. The core element is supported by annular rings 5 cemented to coil form 3. Coil 4 is wound on coil form 3 and together with the core element constitutes an inductance element according to the invention.

For the sake of completeness it may be observed that it is known to manufacture a magnetic core with the aid of a ferrite as the magnetic material by pressing together a pulverulent ferrite and a binding agent, for example an artificial resin, in a manner similar to that in which powdered iron and a binding agent are pressed into mass cores. With such cores moisture can have only a slight harmful effect if the ferrite is protected by the binding agent against the action of moisture. The invention does not relate to such kept together by a binding agent but it relates to magnetic cores consisting of a mass of ferrite which has been sintered together, as may be obtained, for example, by sintering a pulverulent ferrite pressed into a core of the desired shape or by slntering a ferrite-forming mixture of oxides or of compounds which, upon being heated, are converted into oxides, which has been pressed into cores of the desired shape. By a core is meant both a core arranged within a coil and any other component of electromagnetic constructions which is utilized in view of its magnetic properties, for example components lfor magnetical screening.

The term ferrite as employed throughout the specification and the appended .claims refers to a crystalline material which is a compound of the reaction product of a metal oxide vand iron oxide having the empirical formula MFezO4 wherein M represents a bivalent metal. A ferrite" is a salt of the hypothetical ferritic acid H2Fez04 and has excellent magnetic properties, i. e., high permeabilities and low magnetic losses. The ferrite has a crystalline structure and is generally formed by sintering the metal oxide lwith iron oxide at relatively high temperatures, g., at temperatures greater than 1000 C.

While I have disclosed my invention -with specific examples and illustrations, other obvious variations and modifications thereof will be readily apparent to those skilled in the art without departing from the spirit and scope of the invention.

What I claim is:

1. A ferromagnetic core element comprising a porous body of sintered powdery ferrite material, and an adherent envelope of a moisture-excluding material enclosing said body.

2. A ferromagnetic core element comprising a porous body of sintered powdery ferrite material, and an adherent envelope of an electrically-insulating moisture-excluding material enclosing said body.

3. A ferromagnetic core element having a high permeability and low eddy-current and hysteresis losses comprising a porous body lof vsintered powdery ferrite material. and an adherent -envelope of moisture-excluding-waxy paraffin material enclosing said porous body.

4. A ferromagnetic core element having a high permeability and a low eddy-current and hysteresis loss comprising a porous Ibody of sintered powdery ferrite material, and a moisture excluding envelope of a bituminous base moisture impervious material enclosing said porous body.

5. A ferromagnetic core element having a high permeability and a low eddy-current and hysteresis loss comprising a porous body of sintered powdery ferrite material, and a moisture including envelope of an ozokerite base moisture-impervious material enclosing said porous body.

6. A ferromagnetic core element having a high permeability and a low eddy-current and hysteresis loss comprising a porous body of sintered powdery ferrite material, said body being substantially lfree of moisture, and an envelope of moisture-excluding waxy paraffin material enclosing said body.

7. A ferromagnetic core element having a high permeability and a low eddyeourrent and hysteresis loss comprising a porous body of sintered powdery ferrite material, said ferrite body having a loss factor of tg which is less than 0.06 at a frequency not greater than approximately 1000 lic/sec., vksaid body being substantially free of moisture, andan adherent envelope of moistureexcluding waxy paraffin material enclosing said body.

FREDERIK HENDRIK GUSDORF.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,688,478 Weiss Oct. 23, 1928 1,783,560 Eisenmann Dec. 2, 1930 2,191,151 Hale Feb. 20, 1940 2,214,898 Brinkmann Sept. 17, 1940 2,224,934 Schumacher Dec. 17, 1940 2,307,343 Whipple Jan. 5, 1943 2,407,234 Guthrie et al Sept. 10, 1946 FOREIGN PATENTS Number Country Date 463,030 Great Britain Mar. 19, 1937 

1. A FERROMAGNETIC CORE ELEMENT COMPRISING A POROUS BODY OF SINTERED POWDERY FERRITE MATERIAL, AND AN ADHERENT, ENVELOPE OF A MOISTURE-EXCLUDING MATERIAL ENCLOSING SAID BODY. 